In recent years, temperature management has become important in the quality management of products and manufactured articles. For example, if fresh goods such as fresh foods or cut flowers, medicines, and semiconductor materials are not subjected to sufficient temperature management and are exposed to a prescribed temperature or higher, then the quality of the product or goods declines or deteriorates, and furthermore, bacteria may proliferate and decomposition may occur.
Therefore, strict temperature management of products and manufactured articles of this kind must be carried out during transportation and conveyance, as well as during manufacture, and a temperature sensing indicator is used as one means of continuously monitoring temperature management of this kind.
The device described in Patent Reference 1 is proposed as a temperature sensing indicator of this kind. The temperature sensing indicator described in Patent Reference 1 is described here on the basis of FIG. 5 and FIG. 6. In these drawings, reference numeral 51 is a base body, and a wall section 51a which is ring-shaped in plan view is disposed on the upper surface of this base body 1. Moreover, a porous pad 52 is provided on the upper surface of the base body 51 on the inner side of the wall section 51a. This porous pad 52 is saturated with a solution of a dye and a chemical substance which remains in solid phase at or below a critical temperature, and which changes to liquid phase above the critical temperature.
Furthermore, an indicator core 53 is disposed on the upper end face of the wall section 51a. Moreover, the upper portion of the indicator core 53 and the outer circumferential surface of the wall section 51a is covered with a cap 54. This cap 54 has a convex shape, a so-called “dome” shape, and is formed in such a manner that when a prescribed external force is applied, the central portion thereof deforms and depressed into a concave shape. Furthermore, the indicator core 53 is gripped between the cap 54 and the wall section 51a, and the indicator core 53 is thereby held. Adhesive 55 is formed on the rear surface of the base body 51 and furthermore, a release liner 56 is provided so as to cover the adhesive 55.
In a temperature sensing indicator 50 having a composition of this kind, the release liner 56 is peeled away, the base body 51 is affixed to a product or manufactured article, whereupon the user pushes the central portion of the cap 54 in with his or her finger, and the indicator core 53 is thereby made to contact the porous pad 52.
When the product, or the like, to which this temperature sensing indicator 50 has been attached is exposed to a prescribed temperature or higher, then the dye in the porous pad 52 changes from solid to liquid phase, and the colored chemical substance moves from the porous pad 52 to the indicator core 53 due to the density gradient between the indicator core 53 and the porous pad 52. As a result of this, it is possible to judge that the product, or the like, in question has been exposed at least once to an atmosphere at the prescribed temperature or higher, by observing the colored state of the indicator core 53.
However, in a temperature sensing indicator of this kind, there is a risk that, regardless of the storage environment, the dye may change to liquid phase and evaporate with the passage of time, and the solvent of the chemical substance may evaporate, and furthermore, in storing the temperature sensing indicator, it is necessary to manage the temperature of the temperature sensing indicator itself.
Furthermore, in a temperature sensing indicator of this kind, the solvent of the chemical substance also evaporates after operation of the indicator, and hence there is a risk in that the history will be erased.
In order to resolve this, a temperature sensing indicator has been proposed in which a temperature sensing material is encased inside a capsule, as described in Patent Reference 2. This temperature sensing indicator is described here on the basis of FIG. 7 and FIG. 8.
In FIG. 7 and FIG. 8, the temperature sensing indicator 60 comprises a base body 61, a capsule 62, mounted on the base body 61, which encases a so-called colored wax, which is an oil-soluble coloring material, pigment or dye mixed into a straight-chain hydrocarbon or a solid solution consisting of a straight-chain hydrocarbon composition, and filter paper 63 provided so as to cover the capsule 62.
When this temperature sensing indicator 60 is used, the capsule 62 is crushed by being pressed from above the filter paper 63 by the user's finger. As a result of this, if the temperature reaches a prescribed temperature or higher, then the colored wax melts and the oil-soluble coloring material, pigment or dye seeps into the filter paper. Consequently, it can be judged from seeing the colored state of the filter paper 62 whether or not the product in question, or the like, has been exposed at any one time to an environment at the prescribed temperature or higher.
In the temperature sensing indicator 60 described in Patent Reference 2, a so-called colored wax, formed by mixing an oil-soluble coloring material, pigment or dye with a straight-chain hydrocarbon or a solid solution consisting of a hydrocarbon composition is encased inside a capsule and therefore evaporation can be suppressed and the indicator can be managed at normal temperature.    Patent Reference 1: Japanese Examined Patent Publication No. 3-562    Patent Reference 2: Japanese Utility Model Application Publication No. 57-29829
However, since the capsule is simply placed on a planar base body, then when the capsule is pressed by the user with his or her finger, for example, the capsule may become detached, or it may be difficult to break the capsule.
Furthermore, when the capsule is broken, the filter paper may become colored due to determining the temperature of the user's finger and hence there is a risk that the product may be mistakenly judged to have been exposed to an environment at the prescribed temperature or higher.
Moreover, there has also been a problem in that the colored wax evaporated after the capsule has been broken and the temperature sensing indicator has been operated.